Project Summary The objective of this K08 Mentored Clinical Scientist Career Award Application is to facilitate development of essential skills that will allow the candidate to become an academic physician-scientist. The candidate and his mentor have designed a training plan that will include a rigorous research component along with didactic instruction to establish the thought processes and principles necessary for successful career development. Through coursework and practical experience, the candidate will develop a deeper understanding of the complex immune mechanisms that underlie influenza pathogenesis and the host immune response to infection. Through his continued clinical work in the medical intensive care unit, the candidate will have the opportunity to inform his basic research program as well as guide the translation of that work to clinical studies and practice. Influenza and other respiratory viruses cause thousands of cases of Acute Respiratory Distress Syndrome (ARDS) yearly in the United States alone and are a substantial driver of morbidity and mortality worldwide. Despite the availability of antiviral medications for influenza, there remains an urgent need for host- directed therapeutics that limit organ damage and can be deployed in a variety of viral illnesses. The initial response to viral infection centers on the innate immune system including type 1 interferon (IFN) expression from infected cells and responding cells such as macrophages and monocytes. Multiple viral and inflammatory inputs converge on signaling kinases such as TANK-binding kinase 1 (TBK1), and these proteins regulate immunity and inflammation in a highly cell type-specific manner. The function of TBK1 in promoting immunity apart from type 1 IFN expression remains highly undefined. The candidate's data demonstrate that TBK1 function in macrophages and monocytes promote accumulation of inflammatory macrophages in the lung, and that deleting myeloid TBK1 lessens host morbidity while preserving viral control. This novel finding of TBK1 function in macrophages points to the TBK1 axis as a possible druggable target in inflammatory lung disease. This proposal defines the contribution of TBK1 to monocyte- and macrophage-driven inflammation in lung infections with the goal of identifying actionable mechanisms that can be manipulated for host-directed therapeutics. The specific aims will utilize in vivo and in vitro techniques to study monocyte and macrophage function and the molecular aspects of innate immune signaling. In Aim 1, we will determine which monocyte subtype and macrophage subpopulation require TBK1 to enter the lung in influenza infection and examine the transcriptomic consequences of TBK1 function. In Aim 2, we will use mouse models to determine the upstream signals that activate macrophage TBK1 in influenza infection. Finally, in Aim 3 we will use biochemical and proteomic tools to examine the signaling consequences of virus- and chemokine-driven TBK1 activation in monocytes and macrophages. These studies will explore new observations concerning TBK1 function with the ultimate goal of improving patient outcomes in this frequently fatal disease.